CN101970377B

CN101970377B - Fine porosity low-microcracked ceramic honeycombs and methods thereof

Info

Publication number: CN101970377B
Application number: CN2008801239775A
Authority: CN
Inventors: G·A·莫克尔
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2007-11-27
Filing date: 2008-11-17
Publication date: 2013-11-06
Anticipated expiration: 2028-11-17
Also published as: WO2009070218A3; EP2234937B1; EP2586756A1; JP5318881B2; US7704296B2; WO2009070218A2; US20100156010A1; CN101970377A; US8377370B2; EP2234937A2; EP2586756B1; JP2011504869A; US20090137382A1

Abstract

Disclosed are high-porosity cordierite honeycomb substrates having fine pore size, narrow pore size distribution, little or no microcracking, and a high thermal shock resistance. The porous ceramic honeycomb substrates generally include a primary cordierite ceramic phase as defined herein. Also disclosed are methods for making and using the cordierite substrates.

Description

The low-microcracked ceramic honeycomb body of tiny porosity and method thereof

The right of priority in first to file is enjoyed in requirement

The application requires the right of priority of No. the 11/986th, 958, the U. S. application submitted on November 27th, 2007.The full content of the document and all publications mentioned in this article, patent and patent documentation all is incorporated by reference into herein.

Background technology

The present invention relates to porous honeycomb body pottery and manufacture method thereof, more specifically, relate to the porous cordierite honeycomb pottery for catalytic converter and particulate filter (as being used for the aftertreatment of engine exhaust).

Summary of the invention

The invention provides a kind of high porosity cordierite honeycomb base material or diesel particulate filter, it has tiny aperture, described base material or strainer comprise few tiny crack or do not contain tiny crack, even in the situation that when not existing tiny crack expection to cause thermal expansivity to increase, still can keep high-heat resistance shock resistant.

The invention provides some honeycombs, it has improved intensity, make it become to make substrate for catalytic converters with following character or the splendid selection of diesel particulate filter (DPF): described substrate for catalytic converters or diesel particulate filter have wall as thin as a wafer, also have simultaneously (if necessary) low cell densities, be used for reducing back pressure and thermal mass (more fast ignition).Described improved intensity can also be made the ceramic body with higher porosity, be used for convertor base material and DPF, be used for further reducing thermal mass or store a large amount of catalyzer (DPF that for example is used for SCR or 4 tunnel catalysis), keep simultaneously enough intensity.The tiny mean pore sizes of honeycomb of the present invention has promoted high strength, and filtration efficiency can additionally be provided in DPF, and the goods that make have the ability of the very tiny particle of improved filtration in the commitment process of soot deposit.

In some embodiments, described porous ceramic honeycombs comprises main cordierite ceramic phase usually, and porosity %P is at least 50%; Mean pore sizes d ₅₀Less than 10.0 microns; Thermal shock parameter (TSP) is at least 450 ℃; Elastic modulus E-ratio, E _{900 ℃}/ E _{25 ℃}, be not more than 1.01.Thermal shock parameter TSP is defined as (MOR _{25 ℃}/ E _{25 ℃}) (CTE _{500-900 ℃}) ^-1, MOR _{25 ℃}4 modulus of the breaking tenacity of 25 ℃, E _{25 ℃}The Young's modulus of elasticity of 25 ℃, E _{900 ℃}In heat-processed, at 900 ℃ of Young's modulus that record, CTE _{500-900 ℃}It is the high temperature thermal expansivity at 500-900 ℃.

In some embodiments, the present invention also provides a kind of method that is used for preparing porous ceramic honeycombs structure as herein described.Described method comprises substantially: inorganic raw material, organic binder bond and liquid carrier are mixed, form the batch of material of plasticising, form the green compact body, dry described green compact body by the batch of material of described plasticising, described green compact body is fired, described cordierite ceramic structure is provided.

Partly proposed the other embodiment of disclosure in following detailed description and any claim, they partly are derived from detailed description, maybe can understand by implementing the present invention.Above general introduction and following detailed description are only Illustrative, can not be construed as limiting.

Brief Description Of Drawings

Accompanying drawing has shown some embodiment of the present invention.

Fig. 1 be low-microcracked cordierite honeycomb bodies of the present invention during heating and cooling Young's modulus (psi) and temperature (℃) graph of a relation.

Fig. 2 be the cordierite honeycomb bodies of height tiny crack during heating and cooling Young's modulus (psi) and temperature (℃) graph of a relation.

Fig. 3 is the isometric view of porous honeycomb body base material.

Fig. 4 is the isometric view of porous honeycomb body strainer.

Fig. 5 is low-microcracked trichroite embodiment of the present invention (black circle) and has low porosity (MOR _{25 ℃}/ E _{25 ℃}) and the strain tolerance level (MOR/E) of the relatively poor example (soft dot) of medium porosity _{25 ℃}Graph of a relation with porosity %.

Embodiment

Describe the various embodiments of disclosure in detail referring to accompanying drawing.Reference to various embodiments does not limit the scope of the invention, and the scope of the invention only is subjected to the restriction of the scope of appended claims.In addition, all examples of listing in this manual all are not intended to be construed as limiting, and are only to list prescription of the present invention many some embodiments in may embodiments.

Material, compound, composition and the component of the product of the preparation of the method and composition that disclosed the method and composition that can be used for disclosing, can use in conjunction with the method and composition that discloses, can be used for disclosing or the method and composition that discloses.Disclosed in this article the material of these and other, be to be understood that, combination, subset, mutual relationship, the group of these materials have been disclosed, etc. and when not disclosing clearly the permutation and combination of the concrete reference of each different independent and combination set and these compounds, specifically imagine in this article and described each in them.Therefore, if disclose a class substituent A, B and C and disclose the example of the embodiment A-D of a class substituent D, E and F and combination, can be individually and jointly imagine each.Therefore, in this example, specifically imagined following combination A-E, A-F, B-D, B-E, B-F, C-D, each in C-E and C-F should think that above these are all from A, B and C; D, E and F; And the content illustration of example combination A-D.Equally, also specifically imagine and disclosed above-mentioned any subset or combination.Therefore, for example, specifically imagined A-E, the subgroup of B-F and C-E, and should think that they are from A, B and C; D, E and F; And the content illustration of example combination A-D.This conception of species is applied to all aspects of this content, comprises the preparation method of any component of composition and the composition that discloses and each step in using method.Therefore, if there are a plurality of additional steps that can carry out, be to be understood that can be by disclosed method arbitrary specific implementations or the combination of embodiment carry out each in these additional steps, and can specifically imagine each such combination and will be understood that it is disclosed.

Porous cordierite ceramic honeycomb structure with high-heat resistance shock resistant and tiny aperture can be used for controlling the device that pollutes, for example substrate for catalytic converters, SCR base material and some diesel particulate filter (DPF).In these were used, the hole in base material provided a kind of and " has fixed " on the conduit wall surface external coating (EC) or catalyzer or the mode within conduit wall, for DPF, is from the waste gas filtering fine particles.In history, people are by keeping low thermal expansivity (CTE) to realize the high-heat resistance shock resistant of cordierite honeycomb bodies pottery, described low thermal expansivity is achieved in the following ways: make cordierite crystal produce tiny crack and texture orientation, make the thermal expansion z axle (also referred to as c-axis) of its negative sense be orientated in the plane of honeycomb wall.For the thermal expansivity of further making great efforts to keep low, method before mainly is primarily focused on the very low high-purity raw such as the constituent content that uses sodium, potassium, calcium, iron, to reduce as far as possible existing of less important phase, particularly glassy phase.

Recently the trend of petrol engine exhaust after-treatment is that catalytic converter is had higher requirement.Specifically, people need per unit volume to have low-qualityer convertor, because such convertor can heat quickly, earlier begin waste gas is carried out catalyzed conversion, make thus the overall contamination of discharge in the driving circulation still less.Can be with low cell densities, realize lower quality than the arbitrary combination of thin-walled or higher porosity, these practices all can reduce the intensity of convertor base material.Realize that in the inferior quality cordierite honeycomb bodies still there is challenge in high strength, this is that tiny crack is essential in order to realize extremely hanging down CTE because wherein have tiny crack, and this also can cause the intensity of pottery to reduce.In DPF, when DPF is carried out catalysis, often need higher porosity.Similarly, this higher porosity also can reduce the intensity of DPF.

Second challenge that the catalyst substrates that is comprised of the cordierite ceramic of tiny crack or DPF face is; very tiny catalyzer external coating (EC) particle can infiltrate through in tiny crack in trichroite matrix, perhaps makes the component from the dissolving of external coating (EC) and catalyst system be precipitated in tiny crack.In DPF, also might make dust or soot particles enter tiny crack.Being present in the closure that particle in tiny crack may disturb tiny crack between heating period, is mainly as the pin plug, crackle to be opened wide.This may cause thermal expansivity (CTE) to increase, and also may make Young's modulus (E) increase, and these two kinds of factors all can cause heat-shock resistance to reduce.

Although reduce thermal expansivity for the effort that improves heat-shock resistance mainly concentrates on before, also can improve by increasing intensity (for example weighing by rupture modulus) and the ratio MOR/E of Young's modulus of elasticity the heat-shock resistance of stupalith.Value MOR/E is also referred to as the strain tolerance level of pottery.

In some embodiments, the invention provides high porosity cordierite honeycomb base material or DPF with tiny aperture, it comprises few tiny crack or there is no tiny crack, even in the situation that when not existing tiny crack that problem that thermal expansivity increases occurs, also can keep high-heat resistance shock resistant.This base material has improved intensity, also has there is the less heat-shock resistance of susceptibility in external coating (EC) and catalyzer.

" comprise ", " comprising " or similar terms represent to include but not limited to.

" one " of singulative, " a kind of " and " being somebody's turn to do " comprise the thing that refers to of plural number, unless other clearly expression is arranged in text.Therefore, for example, mention " component " and comprise the aspect with two or more these class components, unless other clearly expression is arranged in text.

Event or situation meeting that " optional " or " randomly " expression is described subsequently or can not occur, and this description comprises the example that the example of event or situation generation and event or situation do not occur.For example, " optional component " represents that this component can exist or not exist, and this description comprises two aspects that the present invention includes described component and get rid of described component.

In this article, scope can be expressed as from " approximately " occurrence and/or to " approximately " another occurrence.When such a scope of expression, another embodiment comprises from an occurrence and/or to another occurrence.Similarly, when using prefix " approximately " expression numerical value as approximation, should be understood that concrete numerical value forms another aspect.No matter the end value of each scope is connect with another end value or be independent of another end value, is all significant.

Unless concrete phase antirepresentation is arranged, otherwise, represent that such as " % by weight " that represent component or " weight percentage " or terms such as " weight percents " weight of this component of being expressed as a percentage is with respect to the ratio of the gross weight of the composition that comprises this component.

In some embodiments, described porous ceramic honeycombs has higher porosity.For example, ceramic honeycomb body of the present invention can have overall porosity %P 〉=45%, makes the overall porosity (%P) of porous insert be at least 45%, is at least 50%, is at least 55%.As additional or alternative, ceramic honeycomb body of the present invention can have overall porosity %P 〉=52%, %P 〉=55%, even %P 〉=58%.In some embodiments, ceramic honeycomb body of the present invention can have %P 〉=60%, even %P 〉=65%.

In some embodiments, described high overall porosity can preferably be comprised of the IPN pore network that has than fine pore and narrower pore size distribution.In some embodiments, described tiny aperture is characterized as mean pore sizes (d ₅₀) be no more than 10 microns.For example, described mean pore sizes can be about the 1-10 micron.In some embodiments, described mean pore sizes d ₅₀Can be approximately less than 8 μ m, less than 7 μ m, less than 6 μ m, less than 5 μ m, even approximately less than 4 μ m.One preferred embodiment in, described mean pore sizes can be approximately less than 7.9 microns.

Narrow pore size distribution can provide low soot to load pressure drop, when described main body is used as particulate filter, can obtain filtration efficiency.The relatively narrow degree of the pore size distribution of the hole of porous bodies of the present invention can be by calculating d _fOr d _bCharacterize, wherein d _f=(d ₅₀-d ₁₀)/d ₅₀, d _b=(d ₉₀-d ₁₀)/d ₅₀Parameter d in these equatioies ₁₀, d ₅₀And d ₉₀Be normally defined in this article, measure according to standard mercury porosimeter, the aperture the when difference 10%, 50% of material hole volume and 90% belongs to the hole of small-bore more.Therefore, during these are measured, d ₁₀＜d ₅₀＜d ₉₀In some embodiments, d _fValue can comprise for example d _f≤ 0.55, d _f≤ 0.50, d _f≤ 0.45, d _f≤ 0.40, d _f≤ 0.37, d _f≤ 0.35, d even _f≤ 0.30.

As mentioned above, described narrow pore size distribution can also characterize with the overall width of pore size distribution, uses equation d _b=(d ₉₀-d ₁₀)/d ₅₀Definition.For example, d _bValue can comprise d _b≤ 1.50, d _b≤ 1.20, d _b≤ 1.00, d _b≤ 0.90, d even _b≤ 0.80.

The weather resistance of described ceramic under the thermal shock condition can also characterize by calculating thermal shock parameter (TSP).More particularly, TSP is when the cool region of main body is about 500 ℃, this main body in the situation that do not break the index of tolerant maximum temperature difference.Therefore, for example, if the TSP that calculates is about 450 ℃, expression is when the coldest temperature of some positions in honeycomb is 500 ℃, and the temperature of other position must not be over 950 ℃.Thermal shock parameter calculates according to following equation: TSP=(MOR _{25 ℃}/ E _{25 ℃}) (CTE _{500-900 ℃}) ^-1, MOR in formula _{25 ℃}The breaking tenacity modulus of 25 ℃, E _{25 ℃}The Young's modulus of elasticity of 25 ℃, CTE _{500-900 ℃}It is the mean thermal expansion coefficients of 500 ℃ to 900 ℃.

Rupture modulus MOR records on porous rod by four-point method, and described porous rod is the porous rod that for example is of a size of about 0.5 * 1.0 * 5.0 inches or about 0.25 * 0.5 * 2.5 inches, and its length is parallel to the passage of honeycomb.MOR is the tolerance of the flexible intensity of honeycomb.Need to have high MOR value, this is because this can make main body have higher mechanical endurance and higher heat durability and heat-shock resistance.High MOR value also can obtain higher thermal shock parameter, (MOR _{25 ℃}/ E _{25 ℃}) (CTE _{500-900 ℃}) ^-1

Young's modulus (Young's modulus), E, by the acoustic resonance technical measurement, wherein sample is the rod of 0.5 * 1.0 * 5.0 inches, the length of described rod is parallel to the length of passage.Young's modulus is the tolerance of main body rigidity.Need to have low E value, this is because this can make main body have higher flexible and higher heat durability and heat-shock resistance.Low E value also can obtain higher thermal shock parameter, (MOR _{25 ℃}/ E _{25 ℃}) (CTE _{500-900 ℃}) ^-1

Thermal expansivity CTE uses dilatometry, along the axial mensuration of sample, described sample be axially the direction that is parallel to honeycomb channels length.As mentioned above, CTE _{500-900 ℃}Value be the mean thermal expansion coefficients of 500-900 ℃.Similarly, CTE _{25-800 ℃}Value be the mean thermal expansion coefficients of 25-800 ℃, CTE _{200-1000 ℃}Value be the mean thermal expansion coefficients of 200-1000 ℃, these values are all to measure in the process that sample is heated.People need to obtain low CTE value, in order to obtain high heat durability and heat-shock resistance.Low CTE value also can obtain higher thermal shock parameter, (MOR _{25 ℃}/ E _{25 ℃}) (CTE _{500-900 ℃}) ^-1In some embodiments, CTE _{500-900 ℃}Preferably be not more than 23 * 10 ^-7/ ℃, 22 * 10 ^-7/ ℃, 21 * 10 ^-7/ ℃, 20 * 10 ^-7/ ℃, not even greater than 19 * 10 ^-7/ ℃.

In some embodiments of the present invention, the thermal shock parameter value TSP of preferred honeycomb 〉=450 ℃, TSP 〉=500 ℃, TSP 〉=525 ℃, TSP 〉=550 ℃, even TSP 〉=600 ℃.In some embodiments, the thermal shock parameter value can be TSP 〉=700 ℃, TSP 〉=800 ℃, even TSP 〉=900 ℃.For these example T SP value in embodiment of the present invention, can calculate the thermal shock limit (TSL) of ceramic honeycomb body.As mentioned above, usually being thought of as the thermal shock limit in the ceramic honeycomb body surface temperature is 500 ℃, but crackle when infringement do not occur, the top temperature that the honeycomb center can be heated to.TSL can estimate by add 500 ℃ on thermal shock parameter (TSP), TSL=TSP+500 ℃.

In some embodiments, very most highly interconnected hole comprises the narrow pore size distribution of cordierite honeycomb bodies, can have very important contribution to high strain tolerance level and the high TSP value of gained.The effect that reduces elastic mould value that high hole interconnectivity in these low-microcracked potteries brings is greater than the MOR value.Therefore, strain tolerance level (MOR _{25 ℃}/ E _{25 ℃}) also be denoted as (MOR/E) _{25 ℃}, the value of TSP depends on this strain tolerance level, this strain tolerance level is subject to the preferential impact (Fig. 5) of amount of the porosity of these low-microcracked potteries.In some embodiments, provide higher (MOR/E) _{25 ℃}Ratio, wherein (MOR/E) _{25 ℃}〉=0.10%, (MOR/E) _{25 ℃}〉=0.11%, (MOR/E) _{25 ℃}〉=0.12%, (MOR/E) _{25 ℃}〉=0.13%, (MOR/E) _{25 ℃}〉=0.14%, (MOR/E) _{25 ℃}〉=0.15%, (MOR/E) _{25 ℃}〉=0.16%, even (MOR/E) _{25 ℃}〉=0.17%.

In some embodiments of the present invention, described porous cordierite honeycomb comprises rare-earth oxide.The content of described rare-earth oxide preferably accounts for the 0.25-4.0 % by weight of ceramic body, more preferably 0.5-3.0 % by weight, even more preferably 0.7-2.0 % by weight.Rare earth oxide is yttrium oxide or lanthanum trioxide preferably.Also preferred described rare earth oxide with glassy phase, at least in part with glassy phase, is present in the microstructure of described pottery.Have been found that the intensity that exists rare earth oxide can improve main body, reduce tiny crack.

Honeycomb of the present invention can have microstructure, trichroite crystallite random orientation wherein, perhaps its orientation preferably make negative sense-CTE crystal z-axle is parallel to the plane of honeycomb wall.Need to have this type of orientation of height, axially (in the wall plane, be parallel to the length of passage) and the CTE of (wall plane in, perpendicular to the length of passage) radially because can reduce like this honeycomb.The degree of preferred crystalline orientation is by the x ray diffraction method, measures at the sample under the main body cutting of firing." XRD I ratio " is by relational expression EQ1 definition.

I-ratio=I (110)/[I (110)+I (002)] EQ.1

Wherein I (110) and I (002) use copper K α radiation, based on the hexagonal cells indexing at XRD peak, from the peak height of the XRD diffraction on (110) in the trichroite lattice and (002) plane." axially I-ratio " I _ABe to record on the axial cross section of honeycomb by the x ray diffraction method, so-called axial cross section represents the cross section perpendicular to passage length." transversal I-ratio " I _TBe to measure on the honeycomb wall surface of in accordance with the law firing, removed vertical wall during mensuration." powder I ratio " is to make powder by the honeycomb sample is ground to tiny granularity, measures on this powder.The value of powder I ratio also is expressed as the I ratio of the cordierite crystal of random orientation, is about 0.655.

That cordierite crystal in the honeycomb body structure wall shows Δ near the example of random orientation _I≤ 0.1, Δ wherein _I=I _T-I _AOn the other sidely be that the trichroite crystallite in the wall of low-microcracked honeycomb body structure of the present invention has preferred orientation, can satisfy Δ _I＞0.1.In some embodiments, in porous ceramic honeycombs, the wall with honeycomb body structure of preferred orientation can satisfy I _A≤ 0.60, I _A≤ 0.55, I _A≤ 0.50, I even _A≤ 0.45.In addition, the wall of honeycomb body structure can satisfy I _T〉=0.70, I _T〉=0.75, I _T〉=0.80, I even _T〉=0.85.In some embodiments, the low-microcracked honeycomb body structure with preferred orientation of the present invention can satisfy Δ _I〉=0.2, Δ _I〉=0.3, Δ _I〉=0.4, Δ even _I〉=0.45.

In order to keep good heat-shock resistance, cordierite ceramic honeycomb should be relatively low at the mean thermal expansion coefficients (following is CTE) of 25-800 ℃ of temperature range.Therefore, in some embodiments of the present invention, can so that in ceramic body along the CTE at least one direction≤18.0 * 10 ^-7/ ℃.In some embodiments, CTE≤16.0 * 10 are provided along at least one direction ^-7/ ℃, CTE≤14.0 * 10 even ^-7/ ℃.In some embodiments of low-microcracked honeycomb, described cordierite ceramic honeycomb can be CTE≤12.0 * 10 along the thermal expansivity in this temperature range at least one direction ^-7/ ℃, CTE≤11.0 * 10 even ^-7/ ℃.In some embodiments, can provide approximately 10.5 * 10 ^-7/ ℃ to 18.0 * 10 ^-7/ ℃ CTE, comprise that for example CTE is about 10.5 * 10 ^-7/ ℃ to 14.0 * 10 ^-7/ ℃.In some embodiments, the trichroite crystallite preferably is orientated and comprises that the z axle that makes them is parallel to the plane of wall, makes Δ _I＞0.10, and CTE≤14.0 * 10 ^-7/ ℃.In some embodiments, the trichroite crystallite preferably is orientated and comprises that the z axle that makes them is parallel to the plane of wall.In some embodiments, also preferred CTE is at least 10.5 * 10 ^-7/ ℃, because such CTE value can be brought low tiny crack.For this reason, preferred CTE 〉=12.0 * 10 also ^-7/ ℃.In other embodiment, the orientation of the trichroite crystallite in wall is almost random, makes Δ _I≤ 0.10, CTE can be about 14.0 * 10 ^-7/ ℃ to 18.0 * 10 ^-7/ ℃.

The above CTE value of cordierite ceramic body also can be subject to the impact of following factor, for example: the degree of tiny crack, crystallite orientation is with respect to the wall plane or extrude the degree of orientation (microstructure texture) of direction, and less important crystalline phase, for example amount of spinel, sapphirine, mullite and aluminum oxide (corundum).Therefore, have been found that the CTE that tiny crack causes _{25-800 ℃}The degree Δ CTE that value reduces _mc, can estimate by equation 2 or equation 3:

Δ CTE _mc(I _T)={ 34-26 (I _T)+0.6 (%SCP)-CTE _{25-800 ℃}Equation 2

Δ CTE _mc(I _A)={ 76.838 (I _A) ³-129.5 (I _A) ²+ 97.915 (I _A)-12.8}+0.6 (%SCP)-CTE _{25-800 ℃}Equation 3

In equation 2 and equation 3, I _TAnd I _AHorizontal and axial XRD I-ratio defined above, %SCP is that it equals % by weight spinel+% by weight sapphirine+% by weight mullite+% by weight corundum by the overall weight percent of less important crystalline phase in the ceramic body of firing of powder x ray diffraction method (XRD) mensuration; CTE _{25-800 ℃}Be the thermal expansivity that records that defines as mentioned, unit is 10 ^-7/ ℃; Δ CTE _mc(I _T) and Δ CTE _mc(I _A) unit be 10 ^-7/ ℃.Therefore, if for example record CTE _{25-800 ℃}Be 12.0 * 10 ^-7/ ℃, substitution numerical value " 12.0 " in equation 2 and equation 3.Similarly, if for example by the right side of equation 2 or equation 3 calculate numerical value " 1.5 ", mean Δ CTE _mc(I _T) or Δ CTE _mc(I _A) value be 1.5 * 10 ^-7/ ℃.

Larger (corrigendum) Δ CTE _mc(I _T) and Δ CTE _mc(I _A) the more substantial tiny crack of value representation.If Δ CTE _mc(I _T) or Δ CTE _mc(I _A) value close to zero, the degree of tiny crack is less.In some embodiments, the Δ CTE of calculating _mc(I _T) or Δ CTE _mc(I _A) value may be even negative value slightly, this is due to the less contribution of other less factor to CTE, perhaps due to I-ratio, %SCP or CTE _{25-800 ℃}Calculated value exist less error to cause.According to certain embodiments of the present invention, the feature of described main body can satisfy Δ CTE _mc(I _T) value or Δ CTE _mc(I _A) value less than 3.0 * 10 ^-7/ ℃, be more preferably less than 2.0 * 10 ^-7/ ℃, less than 1.5 * 10 ^-7/ ℃, even less than 1.0 * 10 ^-7/ ℃.

Tiny crack parameter N b ³With E-ratio E _{900 ℃}/ E _{25 ℃}It is the measurement to tiny crack level in ceramic body such as cordierite ceramic.Inventor's discovery, to low-microcracked cordierite bodies, Young's modulus raises and reduces gradually with temperature.It is believed that, reducing of this Young's modulus is because due in crystalline structure, the distance between atom increases with the temperature rising.The Young's modulus of the non-microcracked cordierite honeycomb bodies of porous is shown in Fig. 1 with the example that the temperature rising reduces.Fig. 1 illustrate non-microcracked cordierite honeycomb bodies pottery be heated to 1,200 ℃ (filled circles) and more cooling during getting back to room temperature (solid and hollow square) Young's modulus and the variation relation of temperature performance.In fact the heating and cooling trend curve does not exist tiny crack near overlapping expression.Discovery is from room temperature to 900 ℃, and perhaps even 1000 ℃, reducing of Young's modulus is basic for linear.When being approximately higher than 1,000 ℃, Young's modulus is larger with the speed that the temperature rising reduces.It is believed that its reason is that a small amount of residual glassy phase occurs softening, perhaps partial melting even, glassy phase is react by impurity during ceramic post sintering or add the reaction of the metal oxide that forms glass to form at first.Surprised is, finds to non-microcracked cordierite ceramic the elastic modulus E of Young's modulus during with the velocity of variation Δ E °/Δ T of heating and non-microcracked body room temperature ° _{25 ℃}Be directly proportional, and represent with relational expression 4 approx:

Δ E °/Δ T=-7.5 * 10 ^-5(E ° _{25 ℃}) equation 4

The subscript of its Elastic Modulus item (E °) " ° " the ceramic Young's modulus in non-microcracked attitude of expression.To non-microcracked cordierite bodies, be heated to high temperature as basic identical to compliance and the temperature compliance between initial heating period of temperature in the Young's modulus that carries out cooling period after 1200 ℃, therefore, at any assigned temperature, the elastic mould value of cooling period and its during heating elastic mould value at this temperature are almost identical.This also can be by illustrating shown in low-microcracked cordierite ceramic body in Fig. 1.

Temperature compliance to the Young's modulus of the cordierite ceramic body of height tiny crack is shown in Fig. 2.Therefore, Fig. 2 cordierite honeycomb bodies pottery that tiny crack is shown be heated to 1,200 ℃ (open circles) and more cooling during getting back to room temperature (solid and hollow square) Young's modulus and the variation relation of temperature performance.

In the ceramic body of height tiny crack, Young's modulus increases gradually, then, along with temperature rises to 1,200 ℃, more sharply increases.It is believed that this increase is because tiny crack is again closed with heating, due to final annealing (annealing), make ceramic body reduce gradually unlimited tiny crack at comparatively high temps.The degree that the degree that E increases because tiny crack reduces reduces with heating greater than the E that makes up each cordierite crystal, the object that has high stiffness when causing high temperature.When pottery was cooling from 1,200 ℃, tiny crack did not ftracture at once again, because microstress is at first very little.As a result, Young's modulus is the trend of non-microcracked cordierite bodies at first with cooling trend.During beginning, this increase is sharply, because the viscosity of any liquid or glassy phase increases, may follow respectively because crystallization or devitrification reduce the volume fraction of liquid or glass.In the embodiment of Fig. 2, approximately 1, between 000-700 ℃, E descends more mild increase with temperature may be owing to the Young's modulus of cordierite crystal with cooling increase naturally.Lower than the about temperature of 700 ℃, Young's modulus with cooling generation reducing gradually, is then to reduce faster.This is because tiny crack progressively ftractures again, and reduces the rigidity of pottery.In room temperature, Young's modulus is got back to and is proceeded to the heat cycle of the initial elastic mould value before of 1200 ℃ near pottery.

In cordierite ceramic, the degree of tiny crack is reflected in two features of heating and cooling curve of Young's modulus.A performance of tiny crack degree is Young's modulus from 25 ℃ to 900 ℃ or to the increase degree between the heating period of 1000 ℃, because it is believed that the increase of Young's modulus is closed the causing again by tiny crack.According to equation 4, can calculate the Young's modulus of non-microcracked cordierite bodies when 900 ℃ or 1000 ℃ and the ratio of the non-microcracked cordierite bodies Young's modulus during at 25 ℃, be E _{900 ℃}/ E _{25 ℃}=1+875 (7.5 * 10 ^-5)=0.934 or E _{1000 ℃}/ E _{25 ℃}=1+975 (7.5 * 10 ^-5)=0.927.E° _{900 ℃}/ E ° _{25 ℃}With E ° _{1000 ℃}/ E ° _{25 ℃}Value a baseline is provided, can relatively have the E of the ceramic body of tiny crack with respect to this baseline _{900 ℃}/ E _{25 ℃}And E _{1000 ℃}/ E _{25 ℃}Value.For example, in Fig. 1, E _{900 ℃}/ E _{25 ℃}Ratio be 0.95, E _{1000 ℃}/ E _{25 ℃}Ratio be 0.87, show that the tiny crack degree is extremely low.On the other side, in Fig. 2, the E of heating curve _{900 ℃}/ E _{25 ℃}Ratio is 1.07, E _{1000 ℃}/ E _{25 ℃}Be 1.12.These values are far above there not being the value of expecting in the tiny crack situation fully.Therefore, to the E of cordierite ceramic _{900 ℃}/ E _{25 ℃}Or E _{1000 ℃}/ E _{25 ℃}Value can be with the quantitative measurement of doing the tiny crack degree of room temperature ceramic body.Therefore, according to certain embodiments of the present invention, E _{900 ℃}/ E _{25 °}≤ 1.00, E _{900 ℃}/ E _{25 ℃}≤ 0.99, E _{900 ℃}/ E _{25 ℃}≤ 0.98, E _{900 ℃}/ E _{25 ℃}≤ 0.97, E _{900 ℃}/ E _{25 ℃}≤ 0.96, E _{900 ℃}/ E _{25 ℃}≤ 0.95, E even _{900 ℃}/ E _{25 ℃}≤ 0.94.For this reason, should be noted that the pottery that forms for by 100% trichroite, if ceramic body is not contain tiny crack fully, the E of the accessible minimum of this ceramic body _{900 ℃}/ E _{25 ℃}Value be about 0.93.When also comprising glassy phase in cordierite ceramic body, E _{900 ℃}/ E _{25 ℃}Value even can be less than 0.93, this is because the glass softening E of causing at high temperature _{900 ℃}Reduce.

Another sign of tiny crack degree is the heating curve of Young's modulus and the interval between cooling curve.The quantitative method of this hysteresis phenomenon is based on the lexical or textual analysis of tangent that sample still is in the cooling curve of not crack temperature range when splitting state.In Fig. 2, tangent is shown line segment A-B, and positive point of contact is designated as point " C ".Therefore, the slope of positive tangent equals the Young's modulus of non-microcracked cordierite bodies to the dependence of temperature, as is subjected to the restriction of equation 4.And the value that this positive tangent extension is back to room temperature (some A) approximately is equivalent to the room temperature Young's modulus (if there is no tiny crack under this sample room temperature) of sample, and equals E ° of this sample _{25 ℃}Therefore, drawn the equation of positive tangent by following General Expression equation 5:

E° _Tangent=(E ° _{25 ℃}) { 1-7.5 * 10 ^-5(T-25) } equation 5

Wherein E ° _TangentExpression is along positive tangent, the Young's modulus of non-microcracked ceramic body under each temperature T.

We have designed a kind of analytical procedure, determine E ° by the Young's modulus that experiment in the process of cooling that is heated to after about 1200 ℃ records _{25 ℃}According to this method, will be approximately 1, the Young's modulus observed value that 000-500 ℃ of cooling period records fits to second order polynomial, as with temperature (℃) the variation relation formula.This equation is following form:

E=c+b (T)+a (T ²) equation 6

The upper limit to the temperature range of the experimental measurement elastic mould value that fits to equation 6, if because for example lower than 1000 ℃ the time glassy phase continue obviously softening or form a small amount of liquid and determine that the temperature variant trend of E is at approximately 1000 ℃ or lower than about 1000 ℃ of curvature that demonstration is very high, the described upper limit can further be limited in the temperature lower than 1000 ℃.Equally, lower limit to the temperature range of the experimental measurement elastic mould value that fits to equation 6, if because significantly again ftractureing of tiny crack and determine that the temperature variant trend of E is at approximately 500 ℃ or higher than about 500 ℃ of curvature that demonstration is very high, described lower limit further is limited in the temperature higher than 500 ℃ more than 500 ℃ time for example.Adopt least square regression (least-squares regression) analytical procedure, draw the regression coefficient " a " in equation 6, the value of " b " and " c ".In Fig. 2, represent polynomial fitting to hollow square with the solid-line curve of 500-1000 ℃.

Obtain in the following manner E ° _{25 ℃}Value: solve Young's modulus and the temperature by the polynomial curve joining of the Young's modulus data fitting of cooling period that draw at the positive tangent that is drawn by equation 5 and equation 6.Be expressed as respectively E at the Young's modulus of this joining and the value of temperature _iAnd T _iIn the embodiment of Fig. 2, E _iAnd T _iValue corresponding to this trilateral, namely put C.Share because this joining is positive tangent and polynomial curve, observe following formula:

E _i=(E ° _{25 ℃}) { 1-7.5 * 10 ^-5(T _i-25) }=c+b (T _i)+a (T _i ²) equation 7

In addition, in points of tangency, the slope of polynomial curve must equal the slope of positive tangent.Therefore, observe following formula:

(E ° _{25 ℃}) (7.5 * 10 ^-5)=b+2a (T _i) equation 8

Equation 7 and equation 8 provide two with two unknown quantity E ° _{25 ℃}And T _iRelated equation.For solving E ° _{25 ℃}And T _i, at first equation 8 is reset, draw:

(E ° _{25 ℃})={ b+2a (T _i)/(7.5 * 10 ^-5) equation 9

Then with equation 9 substitution equatioies 7, draw following formula:

{ { b+2a (T _i)/(7.5 * 10 ^-5) { 1-7.5 * 10 ^-5(T _i-25) }=c+b (T _i)+a (T _i ²) equation 10

Equation 10 is reset, is drawn following formula:

0={c+b (T _i)+a (T _i ²)-{ { b+2a (T _i)/(7.5 * 10 ^-5) { 1-7.5 * 10 ^-5(T _i-25) } equation 11

Every in set equation 11, draw following relational expression:

0＝{c-{b/(-7.5×10 ^-5)}{1+7.5×10 ^-5(25)}}

+(T _i)(b)-(T _i){2a/(-7.5×10 ^-5)}{1+7.5×10 ^-5(25)}

-(T _i){{b/(-7.5×10 ^-5)}{-7.5×10 ^-5}}

+(T _i ²){a-{2a/(-7.5×10 ^-5)}(-7.5×10 ^-5)}

Equation 12

Further simplify equation 12, obtain following formula:

0={c-{b/ (7.5 * 10 ^-5) { 1+7.5 * 10 ^-5(25) } }+(T _i) { 2a/ (7.5 * 10 ^-5) { 1+7.5 * 10 ^-5(25) }+(T _i ²) (a) equation 13

Equation 13 can be expressed as again

0=C+B (T _i)+A (T _i ²) equation 14

In formula, C={c-{b/ (7.5 * 10 ^-5) { 1+7.5 * 10 ^-5(25) } }, B={-2a/ (7.5 * 10 ^-5) { 1+7.5 * 10 ^-5And A=-a (25) }.Then, by solving this quadratic equation, draw T _iValue:

T _i={ B+{B ²-4 (A) (C) } ^0.5}/2A equation 15

T _i={ B-{B ²-4 (A) (C) } ^0.5}/2A equation 16

Equation 15 and equation 16 provide two possible T _iValue wherein only has one to have the physics actual value, namely at 25-1, and 200 ℃ of values that scope is interior.Then, with the T that calculates in this manner _iPhysics actual value substitution equation 9, calculate E ° by equation 9 _{25 ℃}Value.

Solve E ° _{25 ℃}After value, to supposing that non-microcracked sample is at the elastic modulus E of 25 ℃ ° _{25 ℃}With the crack sample that splits at 25 ℃ of actual elastic mould value E that record _{25 ℃}Ratio and the original sample crack degree of splitting before heating be directly proportional.That is, room temperature tiny crack degree reduces E than conference _{25 ℃}Therefore value improves E ° _{25 ℃}/ E _{25 ℃}Value.

Modeling to the relation between Young's modulus and tiny crack provides E ° _{25 ℃}/ E _{25 ℃}Ratio and Nb ³Relational expression between quantity, wherein N is the tiny crack quantity in the unit volume pottery, b be tiny crack diameter (referring to D.P.H.Hasselman and J.P.Singh " the crack brittle ceramic thermal stress resistance analysis of splitting (Analysis of the Thermal Stress Resistance of Microcracked Brittle Ceramics); " Am.Ceram.Soc.Bull., 58 (9) 856-60 (1979) .) particularly, this relation can be expressed as following formula:

Nb ³{ (E ° of=(9/16) _{25 ℃}/ E _{25 ℃})-1} equation 17

Although according to many simplification and assumptions, Nb ³Quantity (being called " tiny crack parameter " herein) provides the another kind of useful mode quantitative to tiny crack degree in ceramic body.To without fine fisssure body, Nb ³Value is 0.00.In the example of Fig. 2, Nb ³Value is 0.184.Therefore in some embodiments, preferred Nb ³Value≤0.08.In some embodiments, the more preferably tiny crack parameter N b of ceramic honeycomb body ³≤ 0.07, Nb ³≤ 0.06, Nb ³≤ 0.05, Nb ³≤ 0.04, Nb ³≤ 0.03, Nb even ³≤ 0.02.

In preferred embodiment, the porosity of cordierite honeycomb bodies is at least 55%, and mean pore sizes is not more than 5 microns, and the thermal shock limit TSL of prediction is at least 1100 ℃, more preferably is at least 1200 ℃.In these embodiments, ceramic honeycomb body also satisfies at least a in following character: 1) E _{900 ℃}/ E _{25 ℃}Value be not more than approximately 0.95; 2) tiny crack parameter N b ³Value be not more than 0.02; 3) Δ CTE _mc(I _T) or Δ CTE _mc(I _A) value be not more than 2.0 * 10 ^-7/ ℃.This exemplary honeycomb is suitable as the inferior quality substrate for catalytic converters very much.

Other preferred embodiment in, the porosity of ceramic honeycomb body is at least 55%, mean pore sizes is the 5-10 micron, the thermal shock limit TSL that estimates is at least 1100 ℃, more preferably be at least 1200 ℃, more preferably be at least 1300 ℃, also comprise at least a in following character: 1) E _{900 ℃}/ E _{25 ℃}Value is not more than approximately 0.95; 2) tiny crack parameter N b ³Value be not more than 0.02; 3) Δ CTE _mc(I _T) or Δ CTE _mc(I _A) value be not more than 2.0 * 10 ^-7/ ℃.These ceramic honeycomb bodies are suitable as diesel particulate filter very much, are used for the application of high filtration efficiency.

Ceramic honeycomb body can be the porous cordierite ceramic honeycomb with many ducts of extending between first end and the second end, for example, and as shown in Figure 3 and Figure 4.Shown in the honeycomb body structure that has of ceramic honeycomb body be suitable for for example circulating catalyst substrate or wall stream exhaust gas particle strainer, as diesel particulate filter.Be shown in Fig. 3 according to the typical porous ceramic honeycombs circulation substrate article 10 of embodiment of the present invention, these goods comprise the duct 11 of many almost parallels, described duct is formed and at least part of being limited by it by the cell walls 14 (perhaps being called " reticulated structure ") of intersecting, and extends to the second end 13 from first end 12.Duct 11 is not stopped up, and directly flows through this duct 11 to second ends 13 downwards from first end 12.Preferably, honeycomb article 10 also is included in the smooth layer of extruding 15 that forms around this honeycomb body structure, and still, this top layer is chosen wantonly, can form as after-applied top layer in the processing of back.In some embodiments, the wall thickness that is used for each cell walls 14 of base material can be for example about 0.002-0.010 inch (approximately 51-254 micron).Cell densities for example is about 300-900 hole/inch ²(cpsi).In preferred embodiment, the porous honeycomb body structure is comprised of many parallel ducts 11, forms honeycomb body structure, and the cross section in described duct 11 is square roughly.Perhaps, also can use other cross-sectional configuration in honeycomb body structure, comprise rectangle, circle, ellipse, trilateral, octagon, hexagon, or their combination.The syndeton in the duct of the longitudinal extension that " honeycomb " expression is formed by cell walls is comprising the pattern of repetition substantially.

Fig. 4 shows the honeycomb filter 100 of some embodiments of the present invention.This generality structure is identical with the circulation base material, comprises the main body 101 that is made of intersection porous ceramic walls 106, and described porous wall 106 extends to the second end 104 from first end 102.Import duct 108 is appointed as in a part of duct, outlet duct 110 is appointed as in some other duct.In strainer 100, comprise tamper 112 in some selected ducts.Generally speaking, tamper is arranged on the end in duct, and with specific arranged in patterns, as directed halma board pattern.Import duct 108 can be stopped up at exit end 104, and exporting duct 110 can stop up at entrance end 102.Other plug pattern can be used, for gaining in strength, all ducts (as shown in the figure) of outermost peripheral can be stopped up.Perhaps, some duct can be stopped up in other positions not in the end.In some embodiments, some ducts can be flow passage, and some ducts can be stopped up, with the design that provides so-called part to filter.In some embodiments, the wall thickness that is used for each cell walls 14 of strainer can be for example about 0.006-0.030 inch (approximately 152-762 micron).Cell densities is for example 100-400 hole/inch ²(cpsi).

So-called cordierite ceramic body or honeycomb represent mainly by Mg ₂Al ₄Si ₅O ₁₈The cordierite composition that forms.But cordierite body can also comprise the composition with similar physical character, and for example " filling " trichroite forms.The trichroite of filling is to comprise for example H in the passage site of trichroite lattice ₂O, CO ₂, Li, K, Na, Rb, Cs, Ca, Sr, Ba, the molecule of Y or lanthanon or the trichroite of element.These components can be brought the character of improvement, for example improve thermal expansion or the thermal expansion anisotropy of sinterability or reduction lattice, and these character can be used for some application.Also comprise and followingly basic trichroite component is carried out Fe because of some reason, Mn, Co, Ni, Zn, Ga, the chemistry of the elements such as Ge replaces the trichroite that consists of, and described reason is for example the character such as improved sinterability, color, electrical property, catalytic property.The symmetry of the lattice of trichroite phase can be that for example Symmetric Orthogonal, six sides are symmetrical, perhaps comprises any mixing of these two kinds of symmetric phases.

In some embodiments, the present invention also provides a kind of method that is used for preparing above-mentioned porous cordierite ceramic honeycomb structure, by inorganic powder batch mixtures and at least a glass formation metal oxide source, organic binder bond and liquid carrier are mixed, provide the precursor batch of the formation pottery of plasticising.The batch of material of plasticising may further include one or more optional components, comprises pore former, softening agent and lubricant.Then, with the batch of material of plasticising by as extrusion molding, the formation green honeycomb.Then, dry these green honeycomb as dry by microwave or RF, are cured in kiln, with the whole cordierite ceramic honeycomb of inorganic raw material source sintering or reaction-sinter into.Described green compact body is fired time enough at enough temperature, so that the cordierite honeycomb bodies of sintering to be provided, described honeycomb comprises lower tiny crack and higher heat-shock resistance.

Described inorganic powder batch can comprise the mixture of the feed composition that forms trichroite, and this mixture can heat under the condition that main sintered phase cordierite composition can effectively be provided.The batch of material feed composition of described formation trichroite can comprise for example magnesium oxide source; Alumina source; And silica source.For example, can select inorganic ceramic powder batch composition, so that a kind of cordierite composition to be provided, said composition is mainly composed of the following components: the about SiO of 49-53 % by weight ₂, the about Al of 33-38 % by weight ₂O ₃With the about MgO of 12-16 % by weight.

Exemplary magnesium oxide source can comprise talcum.In another embodiment, suitable talcum can have approximately the median particle diameter less than 15 microns, even approximately less than 10 microns.Granularity is measured by laser diffraction technology, for example uses

Particle size analyzer.The available example of business that is suitable for the magnesium oxide source of content of the present invention comprises the Lu Zenaka (Luzenac of company available from the AudioCodes Weir of Ontario, Canada, Inc.of Oakville, Ontario, Canada) Artic Mist Talc and from the Montana, the Barret mineral company of enlightening dragon (Barrett ' s Minerals, Inc.ofDillon, Montana) 96-67Talc.

Exemplary alumina source comprises that aluminum oxide forms the source, and it is to form the oxidation Aluminum Compounds in heating.Aluminum oxide formation source comprises: corundum or Alpha-alumina, gama-alumina, transitional alumina, the aluminium hydroxide of gibbsite and bayerite and so on, boehmite, diaspore, aluminum isopropylate etc.The median particle of alumina source comprises that preferably less than 8 microns for example median particle is less than 7 microns, less than 6 microns, less than 5 microns, less than 4 microns, less than 3 microns, less than 2 microns, even less than 1 micron.The available alumina source of business can comprise relatively thick aluminum oxide, and for example Alcan C-700 is serial, and its granularity is about the 4-6 micron, and specific surface area is about 0.5-1 rice ²/ gram is as C-701 ^TM, and relatively thin aluminum oxide, its granularity is about the 0.5-4 micron, as A1000SGD and the A3000 that can obtain from Ao Matisi company (Almatis).

If necessary, alumina source can also comprise that dispersible aluminum oxide forms the source.It can be significantly to be dispersed at least the aluminum oxide formation source that the neutralization of solvent or liquid medium can be used to be provided at the colloidal suspension liquid in solvent or liquid medium that dispersible aluminum oxide forms the source.In one embodiment, dispersible alumina source can be the alumina source of relative high surface area, and its specific surface area is at least 20 meters ²/ gram.Perhaps, the specific surface area of dispersible alumina source is at least 50 meters ²/ gram.In an illustrative embodiments, the dispersible alumina source that is suitable for the inventive method comprises Alpha-hydroxy aluminum oxide (aluminum oxide hydroxide) (AlOOHxH ₂O), so-called boehmite, pseudobochmite and as a hydrated aluminum.In the exemplary embodiment, dispersible alumina source comprise so-called transition or activation aluminum oxide (that is, hydrogen oxide aluminum oxide (aluminum oxyhydroxide) and

, η-, ρ-, ι-, κ-, γ-, δ-and θ-aluminum oxide), they can comprise the water that passes through the chemical mode combination or the hydroxy functional group of various content.The object lesson that can be used for commercially available dispersible alumina source of the present invention comprises Dispal 18N4-80, and it can be available from Sa Suoer North American Corp. (Sasol North America).

Suitable silica source can comprise for example one or more clays, for example gives birth to kaolin, calcined kaolin, perhaps their mixture.In some embodiments, the median particle diameter of described silica source even is more preferably less than 10 microns preferably less than 15 microns.Exemplary clay comprises that for example non-stratiform is given birth to kaolin, and its granularity is about the 7-9 micron, and surface-area is about 5-7 rice ²/ gram, for example Hydrite MP ^TM, and those granularities are about the 2-5 micron, surface-area is about 10-14 rice ²The non-stratiform of/gram is given birth to kaolin, for example Hydrite PX ^TMAnd granularity is about the 1-3 micron, surface-area is about 13-17 rice ²The delaminated kaoline of/gram, for example KAOPAQUE-10 ^TM, perhaps calcined clay, its median particle diameter is about the 1-3 micron, and surface-area is about 6-8 rice ²/ gram, for example Glomax LL.The material of all above titles is all buied from Imerys mining company.In some embodiments of the present invention, when comprising kaolin or calcined kaolin in the batch composition of plasticising, wherein median particle diameter is less than approximately the amount of 7 microns is preferred approximately less than 5 % by weight of inorganic raw material, more preferably at least substantially do not contain described median particle diameter less than about this component of 7 microns in batch composition.Further do not contain the kaolin of any kaolin or calcining in the preferred feedstock mixture.

In some embodiments, raw mix comprises silicon oxide and forms the source, this means to comprise＞95% SiO ₂Material, perhaps can be converted in heat-processed＞95% SiO ₂Material.Described silicon oxide forms the source can further comprise crystalline silica, for example quartz or cristobalite, non-crystalline state silicon oxide, for example fused silica or sol-gel silicon oxide, silicone resin, zeolite, diatomite silicon oxide and similar material.Commercially available quartzy silicon oxide forms the source for example can comprise Imsil A25 silicon oxide available from excellent Ni Min company (Unimin Corporation).In embodiment, silicon oxide forms the compound that can form the free oxygen SiClx when source can comprise heating, for example, and silicic acid or silicon organometallic compound.

Except the batch ingredients of the former trichroite of above-mentioned formation, described inorganic powder batch composition can also comprise one or more cordierite powders that react in advance or synthetic aluminum magnesium silicate glass powder.When selecting cordierite powder or synthetic aluminum magnesium silicate glass powder to be used for batch of material, the median particle diameter of described particle preferably is not more than 30 microns, (D ₉₀-D ₁₀)/D ₅₀Value be not more than 1.20.D ₁₀, D ₅₀(median particle diameter) and D ₉₀In particle volume, the particle diameter of 10%, 50% and 90% powder in the size-grade distribution of measuring by laser diffraction technology.

The cordierite composition of reaction in advance that is suitable in inorganic powder batch can be buied from known source, for example comprises Corning Corp. (Corning Incorporated, Corning, NY, USA) that New York, United States is healthy and free from worry.Perhaps, suitable cordierite composition can also be made in the following manner: the batch composition that forms trichroite effectively being converted under the condition of sintered phase cordierite, heat as mentioned above said composition.In one embodiment, the trichroite of suitable reaction in advance is mainly composed of the following components: about 49-53 % by weight SiO ₂, about 33-38 % by weight Al ₂O ₃With about 12-16 % by weight MgO.The cordierite powder that is fit to predetermined purpose can for example obtain in the following manner: make the inorganic precursor material (comprise mineral assemblage, as clay+talcum+aluminum oxide, spinel+silicon oxide, magnesium oxide+aluminum oxide+silicon oxide etc.) carry out wholly or in part pre-reaction, perhaps make partially or completely devitrification (crystallization) of aluminium-magnesium silicate glass material; Perhaps make the aluminium of chemical precipitation-Magnesium Silicate q-agent material such as partially or completely crystallization of collosol and gel powder.Perhaps, can use the trichroite of natural generation, they are crushed to suitable granularity.

When making the inorganic mineral raw material reaction or preparing cordierite powder by the material of chemical precipitation, for example can form in the following manner: the precursor that preparation mixes or the object of chemical precipitation, heat this object to the temperature that is enough to form trichroite, then this object is pulverized, reached required granularity by optional screening or air classification.Perhaps, raw material or throw out also can carry out pre-efflorescence by nodularization, for example by spraying drying or other atomising methods, the particulate that produces are heated to effectively form the temperature of trichroite.When preparing cordierite powder by glass precursor, melten glass is configured as easily shape and pulverizes, perhaps by being poured in quench liquid such as water, melten glass carries out " swashing broken (drigaged) ".Then select suitably essential size range by optional screening or air classification, the glass feed that forms is crushed to desired particle size.

In some embodiments, described raw mix can further comprise the metal oxide source of at least a formation glass.The metal oxide source of described formation glass can be colloidal metal oxide source, and it can form colloidal suspension in solvent, and this colloidal state oxide source preferably comprises 0-97 % by weight SiO ₂, 0-97 % by weight MgO, 0-97 % by weight Al ₂O ₃, and one or more metal oxides of group under being selected from of at least 3.0 % by weight: Li ₂O, Na ₂O, K ₂O, CaO, Fe ₂O ₃And TiO ₂Described metal oxide can comprise at least 4%, at least 5%, perhaps the colloidal metal oxide source of at least 6 % by weight even.In some embodiments, described colloidal metal oxide source can comprise and contains at least 50 % by weight SiO ₂Collodial silica salt face (when with anhydrous benchmark calculational chemistry formula).For example, colloidal silicate can be colloidal state phyllosilicate (phyllosilicate), as attapulgite or wilkinite.In addition, in preferred embodiment, the metal oxide source of described formation glass can comprise rare earth element, for example yttrium or lanthanum.

Other components that are present in these batch compositions with small proportion comprise the oxide compound of impurity element or the doping agent of having a mind to, as, calcium, lithium, iron, titanium, sodium, potassium, boron, tungsten, bismuth etc.Ratio to magnesium oxide, aluminum oxide and silicon oxide component in the bulk stock mixture is selected, thereby only form stoichiometric trichroite, perhaps can select, can form some spinel, sapphirine, mullite, forsterite, enstatite or glassy phase.In some embodiments, preferred Li+CaO+Na ₂O+K ₂Any rare earth oxide sum of O+ is at least 0.5 % by weight.

Described batch composition can comprise pore former.Pore former be append thing can account for inorganic raw material weight more than or equal to 30 % by weight, 40 % by weight, 50 % by weight,, perhaps 60 % by weight even.Described pore former can comprise for example graphite, starch, even their combination.Starch can comprise for example W-Gum, Starch rice or potato starch.. in the situation of the combination of using graphite and starch, pore former is as the thing that appends take inorganic raw material 100 % by weight as benchmark, comprises more than or equal to 20% graphite with more than or equal to 10% starch.In embodiments of the present invention, the median particle diameter of described pore former is preferably approximately less than 20 microns, approximately less than 15 microns, even approximately less than 10 microns.

For the batch composition of plasticising of the present invention is provided, the described inorganic powder batch composition that comprises above-mentioned powdered ceramic material, forms metal oxide source and any pore former of glass can be mixed with following component: liquid carrier, organic binder bond and one or more optional shaping additive or processing aids.The processing aid of example or additive can comprise lubricant, tensio-active agent, softening agent and sintering aid.The lubricant of example can comprise hydrocarbon ils, Yatall MA or sodium stearate.

The organic binder bond component can comprise the water-soluble cellulose ether tackiness agent, methylcellulose gum for example, Vltra tears, methylcellulose gum derivative, perhaps their combination.More preferred example comprises methylcellulose gum and Vltra tears.Preferably, the organic binder bond that exists in composition is as appending thing, and its amount is the 0.1-8.0 % by weight of inorganic powder batch composition, and more preferably its amount is the 3-6 % by weight of inorganic powder batch composition.Add organic binder bond can further improve force of cohesion and the plasticity of composition in batch composition.Improved force of cohesion and plasticity can for example be improved the ability that mixture is configured as honeycomb.

Preferably being used for as composition of the present invention provides the liquid carrier of the denseness of flowable or pasty state is water, but also can adopt other suitable provisional organic binder bond to be shown the liquid carrier of solvent action.The content of described liquid vehicle component can change, thus for ceramic batch mixture provide optimized working properties and with this mixture in the consistency of other component.Preferably, liquid carrier adds with the form of appending, and its amount is the 15-60 % by weight of inorganic powder batch composition, more preferably the 20-40 % by weight of inorganic powder batch composition.The liquid ingredient amount that reduces as far as possible in described composition can further reduce undesirable dry shrinkage and crackle formation in drying process.

In exemplary preferred implementation, batch composition of the present invention can comprise for example mixture of following component: median particle diameter be not more than approximately 15 microns contain the magnesium source, median particle diameter is not more than the approximately salic source of 8 microns, median particle diameter is not more than approximately, and the silicon oxide of 15 microns forms the source, median particle diameter is not more than the approximately pore former of 20 microns, and one or more metal oxide sources that can increase the amount of the glassy phase in main body after firing, make Li in the main body after firing ₂O+Na ₂O+K ₂The total amount of O+CaO+ rare earth oxide is at least about 0.5 % by weight.The metal oxide source of described formation glass is the compound of rare earth element preferably, for example yttrium or lanthanum.In addition, with the weighing scale of inorganic raw material, median particle diameter approximately less than the content of any kaolin of 7 microns or calcined kaolin approximately less than 5 % by weight, do not contain this component in preferred batch of material.

In exemplary preferred implementation, batch composition of the present invention can comprise for example mixture of following component: median particle diameter be not more than approximately 15 microns contain the magnesium source, median particle diameter is not more than the approximately salic source of 8 microns, median particle diameter is not more than approximately, and the silicon oxide of 15 microns forms the source, median particle diameter is not more than the approximately pore former of 20 microns, and one or more metal oxide sources that can increase the amount of the glassy phase in main body after firing, make Li in the main body after firing ₂O+Na ₂O+K ₂The total amount of O+CaO+ rare earth oxide is at least about 0.5 % by weight.Described batch composition also comprises trichroite source or the aluminum magnesium silicate glass source of the reaction in advance of about 0.001-5 % by weight.The metal oxide source of described formation glass is the preferably compound of rare earth element, for example yttrium or lanthanum too.In addition, with the weighing scale of inorganic raw material, median particle diameter approximately less than the content of the kaolin of 7 microns or calcined kaolin approximately less than 5 % by weight, do not contain this component in preferred batch of material.

In exemplary preferred implementation, described batch composition comprises the mixture of following component: approximately trichroite source or the aluminum magnesium silicate glass source of the reaction in advance of 5-99 % by weight, its median particle diameter is not more than approximately 30 microns, and (D ₉₀-D ₁₀)/D ₅₀Value is not more than approximately 1.20.Described batch composition also comprises median particle diameter and is not more than the approximately pore former of 20 microns, and one or more median particle diameters are not more than approximately the following component that is selected from of 10 microns: magnesium oxide source, alumina source, silica source; And the metal oxide source that can increase the amount of glassy phase in main body after firing, make Li in the main body after firing ₂O+Na ₂O+K ₂The total amount of O+CaO+ rare earth oxide is at least about 0.5 % by weight.

In preferred embodiment, described batch composition can comprise for example mixture of following component: median particle diameter is not more than the approximately talcum of 10 microns, median particle diameter is not more than the aluminum oxide formation source of 8 microns, median particle diameter is not more than approximately the silicon oxide of 10 microns and forms the source, and the about Y of 0.5-3.0 % by weight ₂O ₃-formation source.Randomly, also comprise one or more pore formers, the median particle diameter of described pore former is not more than approximately 15 microns, take inorganic raw material as 100 weight parts, and approximate 80 weight parts that are up to of the content of described pore former.

For example honeycomb base material shown in Figure 3 can be by being fit to form the ordinary method of monolithic devices honeycomb, formed by the batch of material of plasticising.For example, in one embodiment, adopt the ordinary method of any known ceramics forming, the batch composition of plasticising is formed, make green compact, described ordinary method for example comprises: extrude injection moulding, slip casting, rotational casting, pressurization casting, dry-pressing system etc.In an exemplary embodiment, extrude and can use hydraulic ram to extrude press, or two sections single forcing machines that bore of exhaust, or carry out at the twin screw mixing machine of discharge end connection die head assembly.In a rear situation, can select suitable screw element according to material and other processing condition, to form enough pressure, force the batch of material material to pass through die head.

Then the honeycomb that obtains is carried out drying, fire under the condition that can effectively the green compact composition that is shaped be converted into main sintering phase ceramics composition subsequently.The condition of the green compact body that efficient drying is shaped can comprise the condition that can remove basic at least all liquid supporting agent in the green compact composition.In this article, described " at least substantially all " expression exist before dry at least 95%, at least 98%, at least 99% or even all be removed at least about 99.9% liquid carrier.Exemplary and the nonrestrictive drying conditions that is fit to remove liquid carrier is included under following temperature condition the green honeycomb base material is heated: temperature is at least about 50 ℃, at least about 60 ℃, at least about 70 ℃, at least about 80 ℃, at least about 90 ℃, at least about 100 ℃, at least about 110 ℃, at least about 120 ℃, at least about 130 ℃, at least about 140 ℃, even at least about 150 ℃, be enough at least substantially remove the liquid carrier in the green compact composition duration of heat.In one embodiment, the described condition that can effectively at least substantially remove liquid carrier is included in the green compact body of the temperature heating shaping of at least 60 ℃.In addition, heating can be undertaken by the known method of any conventional, hot-air dry for example, RF, microwave drying, or its combination.

Fig. 4, before or after the green compact body is fired, can use thickener to stop up in a part of duct 110 of the monolithic devices honeycomb 100 of 102 pairs of formation of entrance end again, and the composition of described thickener is identical or similar with the composition of main body 101.Preferred is stopped up in the end in duct, forms the tamper 112 that the degree of depth is about the 5-20 millimeter, but can change plug depth.Be positioned at exit end 104 places but the also similarly pattern obstruction of a part in not corresponding with the duct of stopping up at entrance end 102 places duct.Therefore, each duct is preferably only at one end stopped up.Preferred arrangement mode is as shown in Figure 4, stops up every a duct with checker board pattern at designated surface.In addition, described import duct and outlet duct can have required shape arbitrarily.But in illustrative embodiments shown in Figure 4, the cross-sectional shape in described duct is normally foursquare.

Then can fire the honeycomb that forms under certain conditions, described firing condition can be converted into inorganic powder batch composition main sintered phase cordierite composition effectively.Exemplary firing condition can be included in about 1340-1435 ℃, more preferably from about under the highest firing temperature of 1375-1425 ℃, the honeycomb green body body be fired about 5-30 hour.

Embodiment

In order to further illustrate principle of the present invention, following examples are provided, make those of ordinary skills understand manufacturing and the evaluation of cordierite honeycomb bodies of the present invention and method thereof fully.Made great efforts to guarantee the accuracy of numerical value (as amount, temperature etc.); But may there be some errors and deviation.Unless otherwise noted, otherwise umber is parts by weight, and temperature is by ℃ expression or an envrionment temperature, and pressure is normal atmosphere or near normal atmosphere.

In following table with example nonrestrictive mode, by embodiment, the present invention is described.Table 1 provides the source of the raw material that is used for embodiment, and the median particle diameter of measuring by laser diffraction technology.Table 2 has been listed the parts by weight of the raw material that is used for preparing the embodiment of the present invention.Table 3 has been listed the character of the embodiment of the present invention, and wherein the z axle of cordierite crystal is arranged in the honeycomb wall plane basically.Table 4 has been listed the character of the embodiment of the present invention, wherein is being close to random cordierite crystal orientation at the honeycomb wall graphic memory.

In Preparation Example, inorganic raw material and pore former and tackiness agent and mix lubricant are got up, in the stainless-steel grinding machine, add entry in powdered mixture, form the batch of material of plasticising.Described batch of material is extruded as the honeycomb of 2 inches diameter, and it comprises about 300-325 duct/inch ²And the about wall of 0.014-0.015 inch, perhaps about 600 duct/inches ²With the about wall of 0.004 inch.The goods of extruding are carried out drying, then in the electrically heated kiln, fire under the temperature shown in table and hold-time condition.Heating rate is enough to prevent goods generation crackle, and this is that those skilled in the art are well-known.In table, mean thermal expansion coefficients, unit are 10 ^-7/ ℃, use dilatometry, measure being parallel on the passage length of the honeycomb article sample of (" axially ").The % porosity is by mercury porosimetry, the percent by volume of the porosity that records in the wall of goods.Term d ₁, d ₂, d ₅, d ₁₀, d ₂₅, d ₅₀, d ₇₅, d ₉₀, d ₉₅, d ₉₈And d ₉₉Expression accounts for total pore volume 1%, 2%, and all less than the aperture in this aperture, unit is micron (10 in the aperture in 5%, 10%, 25%, 50%, 75%, 90%, 95%, 98% and 99% hole ^-6Rice), be also to record by mercury porosimetry.Therefore, d for example ₉₀Be 90% (volume ratio) the hole the aperture all less than the aperture in this aperture (be equivalent to the mercury accumulation infiltrate volume equal total mercury infiltrate volume 10% the time the aperture).Therefore for example satisfy d ₁₀＜d ₅₀＜d ₉₀

In sample after firing, the weight percentage of remaining mullite, spinel+sapphirine and Alpha-alumina is measured by the x ray diffraction method.Why the content of spinel and sapphirine being combined is because be difficult to according to XRD technology used with this two-phase region separately.

Axially XRD I ratio and laterally XRD I ratio such as equation 1 definition use copper K α radiation, measure by the x ray diffraction method.For the cordierite crystal of random orientation, axial and transversal I ratio all is approximately equal to 0.655.

The numerical value of all rupture moduluss (MOR) or flexural strength is all to use four-point method, is being parallel on the axial direction of honeycomb, records on porous rod (1/2 inch * 1/4 inch * 2.75 inches long).The mean value of MOR numerical value ordinary representation in table to 4 to 6 excellent measurement results.Young's modulus numerical value is to use the acoustic resonance technology, is being parallel on the axial direction of honeycomb, records on porous rod (1 inch * 1/2 inch * 5 inches long).Thermal shock parameter TSP is as mentioned before by (MOR _{25 ℃}/ E _{25 ℃}) (CTE _{500-900 ℃}) ^-1Calculate, thermal shock limit TSL is defined as TSP+500 ℃.Also calculated thermal shock parameter TSP*, it is defined as (MOR _{25 ℃}/ E _{25 ℃}) (CTE _{200-1000 ℃}) ^-1, also having calculated thermal shock limit TSL*, it is defined as TSP*+200 ℃.. so the value of TSL* is when main body the coldest zone reaches 200 ℃, and cordierite bodies can tolerate and not produce the expection top temperature of fracture.

The area that the closed front face area CFA of honeycomb is porous ceramic walls accounts for the mark of the area of honeycomb dignity, by wN{2 (N ^-0.5)-W} calculates, and wherein w is wall thickness, and N is cell densities (the duct number of per unit area).Therefore the value of MOR/CFA is the desired value of MOR that comprises the porous ceramics of honeycomb wall.

Table 1. raw material sources and median particle

(1)(D ₉₀-D ₁₀)/D ₅₀＝1.03

(2) comprise approximately 3 % by weight Na ₂O and 1 % by weight Li ₂O

(3) comprise approximately 3 % by weight Fe ₂O ₃With 1.9 % by weight CaO

(4) comprise approximately 3.5 % by weight Fe ₂O ₃, 2.3 % by weight Na ₂O and 0.4 % by weight CaO

The batch composition of table 2. embodiment of the present invention

Table 3. has the character of the embodiment of substantially nonrandom crystalline orientation

Table 4. has the character near the embodiment of random crystalline orientation

The embodiment of the present invention of table 3 has shown the honeycomb that uses the preparation of following component: tiny talcum, aluminum oxide and tiny raw silicon oxide material have added the Y of 1.0 % by weight ₂O ₃, added pore former, wherein lack the kaolin source.Such combination has obtained the tiny crack of low degree, high porosity, and tiny aperture, and thermal shock parameter TSP is at least 450 ℃.In addition, owing to not comprising cordierite powder or aluminum magnesium silicate glass in raw mix, in the ceramic body that causes obtaining, the trichroite crystallite shows the orientation of height, its z axle is parallel to the plane of honeycomb wall, be expressed as axial XRD I-ratio less than 0.60 low numerical value and laterally XRD I-ratio greater than 0.70 high value.Therefore, CTE _{25-800 ℃}The scope of value is only 10.8 * 10 ^-7/ ℃ to 13.2 * 10 ^-7/ ℃.There is hardly hysteresis phenomenon between the Young's modulus heating and cooling curve of Fig. 1, shows that embodiment 4.4 comprises the tiny crack of low degree.The embodiment of the present invention of Fig. 5 has shown that high porosity brings provides high strain tolerance level (MOR/E) _{25 ℃}Benefit.

The embodiment of the present invention 5.1 and 5.2 of table 4 has proved the honeycomb for preparing by the cordierite powder (it has tiny granularity (4.4 microns)) that adds the reaction in advance of 1 % by weight in the mixture that forms source and quartzy and pore former and impure colloidal clay at talcum, aluminum oxide, described impure colloidal clay is one or more in this ceramic body contribution sodium, calcium and iron, increases the amount of the glassy phase in the main body of firing.Made a kind of main body of firing by the cordierite powder that uses reaction in advance, wherein there is no the preferred orientation of trichroite crystallite, its axial XRD I-ratio is greater than 0.60, and laterally XRD I-ratio is less than 0.70, CTE _{25-800 ℃}Be at least 14 * 10 ^-7/ ℃.Embodiment 5.1 and 5.2 has obtained the tiny crack of low degree, high porosity, and tiny aperture, and thermal shock parameter TSP is at least 450 ℃.Embodiment 5.3 uses the cordierite powder preparation of the reaction in advance of 90 % by weight, has wherein added tiny boehmite, kaolin and colloidal clay as the inorganic adhesive phase, has also added pore former to increase porosity.Described colloidal state smectic clays also provides sodium and lithium impurity, the amount of the glassy phase in the main body after firing with increase.Because the granularity of the cordierite powder of reaction is approximately less than 30 microns in advance, the main body after therefore firing has the tiny crack of low degree.In addition, the Unusually narrow particle size distribution due to cordierite powder is expressed as (D ₉₀-D ₁₀)/D ₅₀＜1.20, and because median particle diameter and the cordierite powder of pore former closely mate, therefore final pore size distribution is narrower.It is 454 ℃ that described narrow pore size distribution and high porosity make MOR/E be about 0.10%, TSP.

The applicant has been found that, by comprising tiny kaolin and not containing rare earth oxide or other adds pore former in forming the conventional raw mix of metal oxide source of glass, be enough to the porosity increase is for example surpassed 50%, but can not make the main body with low tiny crack and height strain tolerance level.

In conjunction with above-mentioned various embodiments and technical description the present invention.But, can carry out various changes and modification, within remaining on simultaneously the spirit and scope of disclosure.

Claims

1. porous ceramic honeycombs, it comprises:

Main cordierite ceramic phase, this ceramic phase shows following character:

Mean pore sizes d ₅₀Less than 7.9 microns;

Overall porosity %P is at least 50%;

Strain tolerance level (MOR _{25 ° of C}/ E _{25 ° of C}) be at least 0.10%;

Thermal shock parameter (TSP) is at least 450 ° of C;

Modular ratio E _RatioBe not more than 1.01,

Wherein TSP is (MOR _{25 ° of C}/ E _{25 ° of C}) (CTE _{500-900 ° of C}) ^-1, MOR _{25 ° of C}The breaking tenacity modulus of 25 ℃, E _{25 ° of C}The Young's modulus of elasticity of 25 ℃, CTE _{500-900 ° of C}The high temperature thermal expansivity of 500-900 ℃, E _Ratio=E _{900 ° of C}/ E _{25 ° of C}, E wherein _{900 ° of C}In heat-processed, at the Young's modulus of 900 ℃ of measurements.

2. porous ceramic honeycombs, it comprises:

Main cordierite ceramic phase, this ceramic phase shows following character:

Mean pore sizes d ₅₀Be less than or equal to 5 microns;

E _RatioBe less than or equal to 0.95, wherein E _Ratio=E _{900 ° of C}/ E _{25 ° of C}, E _{900 ° of C}The Young's modulus of elasticity of 900 ℃, E _{25 ° of C}The Young's modulus of elasticity of 25 ℃,

Thermal shock parameter (TSP) is at least 450 ° of C, wherein TSP=(MOR _{25 ° of C}/ E _{25 ° of C}) (CTE _{500-900 ° of C}) ^-1, MOR _{25 ° of C}The breaking tenacity modulus of 25 ℃, CTE _{500-900 ° of C}It is the high temperature thermal expansivity of about 500-900 ℃;

Δ CTE _mc(I _A) be less than or equal to 2.0 * 10 ^-7/ ° C.

3. method for preparing porous ceramic honeycombs as claimed in claim 1,

Described porous ceramic honeycombs comprises main cordierite ceramic phase, the mean pore sizes d of the cordierite ceramic phase that this is main ₅₀Less than 7.9 microns; Overall porosity %P is at least 50%; Strain tolerance level (MOR _{25 ° of C}/ E _{25 ° of C}) be at least 0.10%; Thermal shock parameter (TSP) is at least 450 ° of C; Young's modulus ratio E _{900 ° of C}/ E _{25 ° of C}Be not more than 1.01; TSP=(MOR wherein _{25 ° of C}/ E _{25 ° of C}) (CTE _{500-900 ° of C}) ^-1, MOR _{25 ° of C}The breaking tenacity modulus of 25 ℃, E _{25 ° of C}The Young's modulus of elasticity of 25 ℃, E _{900 ° of C}At 900 ℃ of Young's modulus that record, CTE in heat-processed _{500-900 ° of C}The high temperature thermal expansivity of 500-900 ℃, E _Ratio=E _{900 ° of C}/ E _{25 ° of C}, E wherein _{900 ° of C}In heat-processed, at the Young's modulus of 900 ℃ of measurements;

Described method comprises:

The precursor batch of the formation pottery of plasticising is provided, and said composition comprises:

Inorganic powder batch mixtures, this mixture comprises: median particle diameter D ₅₀Be less than or equal to the magnesium source of 15 microns, median particle diameter D ₅₀The aluminum oxide that is less than or equal to 8 microns forms source, median particle diameter D ₅₀The silicon oxide that is less than or equal to 15 microns forms the source;

The metal oxide source of at least a formation glass of at least 0.5 % by weight, it comprises yttrium source, lanthanum source or their combination;

Organic binder bond;

Liquid carrier;

The precursor batch that forms pottery by plasticising forms the honeycomb green body body; With

Described honeycomb green body body is fired, to form porous ceramic honeycombs.

4. method as claimed in claim 3, is characterized in that, the precursor batch of the formation pottery of described plasticising comprises:

Inorganic powder batch mixtures, this mixture comprises: median particle diameter D ₅₀Be less than or equal to the talcum of 10 microns, median particle diameter D ₅₀The aluminum oxide that is less than or equal to 8 microns forms source, median particle diameter D ₅₀The silicon oxide that is less than or equal to 10 microns forms the source;

The yttrium oxide source of the formation glass of at least 0.5 % by weight;

Optional particulate pore former, its median particle diameter D ₅₀Be less than or equal to 15 microns.